Radio frequency apparatus



April 26, 1966 R. A. DEHN 3,248,595

RADIO FREQUENCY APPARATUS Filed Feb. 16, 1962 Il g3 25 by United StatesPatent O 3,248,595 RADIO FREQUENCY APPARATUS Rudolph A. Deliri,Schenectady, N.Y., assigner to General Electric Company, a corporationof New York Filed Feb. 16, 1962, Ser. No. 173,703 9 Claims. (Cl.S15-5.16)

This invention relates to radio frequency (RF.) apparatus and moreparticularly to new and improved means for combining the operation andoutput of a plurality of space-charge control tubes.

High power levels of microwave frequency electromagnetic wave energy arecustomarily produced by such power tube devices as magnetrons, klystronsand traveling wave tubes. However, these devices require quite highoperating voltages and also require heavy magnetic fields for focusingor other operating effects on electrons within the devices.

Microwave frequency electromagnetic wave energy may also be producedwith space-charge control devices such as the planar electrode tubestructures known to those skilled in the art. Such devices are operativewith relatively low operating potentials, due to the close spacing ofelectrodes within the devices, and require no magnetic field forfocusing or otherwise influencing the electrons. However, the poweroutput of the space-charge control devices heretofore known in the arthas been quite limited and is not comparable to the power levelsproduced by the other devices previously mentioned, such as magnetronsor the like.

It is frequently desirable to have a source of relatively high powerlevel electromagnetic wave energy which does not require the highoperating voltages or the large magnetic fields of the magnetrons,klystrons, traveling wave tubes or the like. For example, such a sourceof power is quite desirable in microwave heating applications includingthe electronic ovens presently being produced which utilize highfrequency energy in the cooking of foods. However, the planar electrodespace-charge control devices known in the art do not providesufficiently high power levels to operate such devices and, accordingly,magnetrons have generally been used for this purpose even though theyrequire high operating voltages and large magnetic iields.

Also, when space-charge control tubes, such as triodes and tetrodes, areoperated in grounded grid fashion, radio frequency energy is required toaccelerate electrons from the cathode across the cathode grid gap. Thisresults in an equivalent positive input conductance in shunt with thecapacitive susceptance of the cathode-grid electrodes. Now, if aplurality of such tubes are to be operated in a periodically loadedwaveguide resonator, the mentioned conductance will make the attenuationin the grid-cathode resonator high; and the radio frequency input signalwill not appear equally at all tubes in the circuit. In order to avoidexcessive attenuation and achieve more uniform excitation of the tubes,the tube input admittance must be appropriately decoupled from thewaveguide resonator.

It is, accordingly, an object of this invention to provide a new andimproved source o-f microwave frequency electromagnetic wave energy.

It is another object of this invention to provide a new and improvedsource of microwave frequency electromagnetic wave energy which isoperable from a relatively low voltage source and which requires nomagnetic lield for operation.

`It is yet another object of this invention to provide new and improvedmeans for combining the operation and output of a plurality ofspace-charge control electron discharge devices including an inputwaveguide resonator periodically loaded by a plurality of such devicesand 3,248,595 Patented Apr. 26, 1966 ice means for effectivelydecoupling the input admittance of the tubes from the resonator, therebyto avoid excess-ive attenuation and to achieve uniform excitation of thetubes by an input signal introduced into the waveguide resonator.

It is a further object of this invention to provide a device forcombining the operation of a plurality of spacecharge control tubes in amanner which affords maximum mode separation and provides forsubstantially the total power handling capabilities of the number ofdevices so combined.

Briefly stated, and in accordance with one embodiment of the invention,radio frequency apparatus is provided which comprises an input resonantwaveguide and an output resonant waveguide. A plurality of equallyspaced space-charge control devices are mounted in the waveguides withthe cathode-grid interaction gaps thereof coupled to the input waveguideand the corresponding concentrically opposite grid-anode interactiongaps thereof coupled to the output waveguide. The grid-anode gaps arecoupled to the output waveguide in a longitudinal plane extendingthrough the center of the output waveguide while the cathod-grid gapsare coupled to the input waveguide in a longitudinal plane which islaterally or transversely spaced from the center of the input waveguide.Provided in each waveguide and each at a point midway between e-achadjacent pair of control devices are a plurality of passive capacitiveelements. The waveguides are thus each periodically loaded by alternateactive and passive capacitive elements and preferably the periodicspacing between adjacent elements is 1A the length of an electromagneticwave in the waveguides when the waveguides are resonated at apredetermined frequency. The devices are biased in the usual mannerknown to those skilled in the space-charge control tube art and astanding electromagnetic wave of the aforementioned predeterminedfrequency is induced in the input waveguide by means of any suitablecoupling device. The standing electromagnetic Wave in the inputresonator controls the emission of electrons from the cathodes of thedevices and the resultant density-modulated electrons traverse thegrid-anode circuit and induce a corresponding standing electromagneticwave in the output waveguide. Suitable means are provided for extractingelectromagnetic wave energy from the output resonant structure. Theoff-center positions of the devices relative to the input waveguideeffectively decouples the input admittance of the devices from thewaveguide. If desired, the space-charge control devices can be eitherconstructed integrally with the waveguides or as separate tubesdetachably mountable in the waveguides.

For a better understanding of my invention, reference may be had in theaccompanying drawing in which:

FIGURE 1 is a sectional view of apparatus constructed according to oneembodiment of the invention;

FIGURE 2 is a view taken along the sectional lines 2 2. of FIGURE l andlooking in the direction of the arrows;

FIGURE 3 is an wdiagram showing a graphical relation between thefrequency of operation of a periodicallyloaded waveguide and the phaseshift per section of such a waveguide;

FIGURE 4 is a sectional view similar to that of FIG- URE l and shows asecond embodiment of the invention; and

FIGURE 5 is a View taken along the lines 5 5 in FIGURE 4 and looking inthe direction of the arrows.

Referring now to FIGURE l, therein is shown radio frequency apparatusconstructed according to one embodiment of the present invention. Thisapparatus includes an input resonator 2 and an output resonator 3.

Each of the resonators comprises an electrically-shorted section of asubstantially rectangular waveguide and the resonators are juxtaposed soas to have a common wall 4 separating the resonators 2 and 3. The inputresonator 2 is provided with suitable input means, such as an inductivecoupling loop 2a, at one end and the output resonator 3 is provided withsuitable output means, such as an inductive coupling loop 3a, at theopposite end.

From the outset, it is to be understood that the waveguides need nothave a rectangular cross-sectional configuration but can be of anydesired cross-section. Also, and as seen in FIGURE 2, the resonators 2and 3 are not vertically aligned but -are relatively offset. The purposeand advantages of this arrangement will be discussed in detailhereinafter.

The upper and lower walls of the resonators 2 and 3 are suitably`apertured to provide sever-al aligned equally spaced tube socketstherein. Positioned in such sockets are space charge control devicesgenerally designated 5. Each device 5 comprises a suitable envelopestructure 6 and constitutes a triode including a cathode 7, a controlgrid 8 Iand an anode 9 which are suitably spaced and mutually insulated.The cathode 7, grid 8 and anode 9 are provided with suitable coaxialcontacts 11, 12 and 13, respectively, which, when the devices 5 areinserted in the sockets in the waveguides, make suitable coaxialelectrical contact with the respective walls of the waveguides.Specifically, the cathode contacts 11 engage the lower wall of the inputwaveguide 2, the grid contacts 12 engage the intermediate, or common,wall 4 and the anode contacts 13 engage the upper wall of the outputwaveguide 3. In this manner the cathode-grid interaction regions (7,`8), or gaps, of the tubes are coupled to the input waveguide forenabling energy exchange interaction between any electromagnetic wave inthe input circuit and electron flow across the grid-cathode space orinteraction gap. The grid-anode interaction regions (8, 9), or gaps, ofthe tubes are similarly coupled to the output waveguide for enablinginducement therein of electromagnetic Wave energy. It is to beunderstood from the foregoing that while the devices 5 are disclosed asdiscrete devices detachably mounted in the waveguide circuits, theycould, if desired, be constructed integrally with the waveguides. Insuch a structure the complete assembly, including the waveguidesections, could be evacuated and hermetically sealed.

Interposed midway between each adjacent pair of devices 5 and yalignedtherewith in both the input and output waveguides is a passive, ordummy, capacitive element 15. Each element 15 in the input section issubstantially identical in capacitance value to each of thecorresponding reaction gaps defined by the cathode-grid and each element15 in the output section is substantially identical in such value toeach corresponding gridanode gap of the devices 5. It is to beunderstood that the capacitance values of the cathode-grid and gridanode values may be of different values dictated by the electronic ofthe devices 5. Also, the spacing between the outermost devices 5 and theend walls of the waveguides is the same as between adjacent devices 5and dummy elements 15. Thus, the waveguides 2 and 3 are each uniformlyperiodically loaded with alternate active and passive capacitiveelements. The elements 15 can be capacitors defined by upstandingconductive posts, as shown, or can be constructed in any suitablealternative manner. The electrical spacing between adjacent active andpassive elements and between the end walls of the resonators and theoutermost capacitive elements is preferably 1A of the loaded waveguidewave length at a predetermined operating frequency which results inelectric field maxima and minima being located, respectively, at thereaction gaps Iand passive elements. This general arrangement of inputand output resonators periodically loaded with alternate active andpassive capacitive gaps of equal value and operation such that the fieldmaxima and minima are located, respectively, at active and capacitygaps, does not constitute the entirety of the present invention which isan improvement thereover, but is the invention disclosed and claimed incopending U.S. application S.N. 173,724 of M. R. Boyd et al. filedconcurrently herewith and assigned to the same assignee as the presentinvention. The present invention involves the combination ofspace-charge control devices and such periodicallyloaded resonators, butalso means for avoiding excessive attenuation of an input signal in aperiodically-loaded input resonator and achieving uniform excitation ofthe space-charge control devices by that input signal.

The operation of the above-described apparatus is as follows: Thespace-charge control devices are operated in a grounded grid fashion,inasmuch as the control grids for the devices are directly connected tothe walls of the resonators. An accelerating direct current field isestablished lbetween each of the grids 8 and the associated anodes 9 inany suitable manner (not shown). The cathodes 7 can -be energized in`any suitable manner, as by the filamentary heaters schematically shown,and so as to emit electrons under the infiuence of an electric field ofthe proper polarity. An input signal is supplied to input resonator 2through the input loop 2a, with the input signal establishing a standingelectromagnetic wave of the aforementioned predetermined freqeuncy inthe input resonator 2. Inasmuch as the end portions of the resonator 1are short circuited, whereby an electric field minimum must there exist,electric field maxima are established at each of the cathode-grid gapsand electric field minima `at each of the passive elements 15. Analternating electric field in accordance with the input signal and ofmaximum magnitude is established between each of the cathodes 7 and itsrespective associated control grid 8. Electrons are emitted from each ofthe cathodes under the influence of the positive half cycles of thealternating signal thereby established and these electrons pass throughthe control grids and enter the grid anode gaps wherein they aresubjected to the accelerating direct current field therein. Thus,bunches of electrons are delivered to each of the anode members inaccordance with the standing input signal wave in the resonator 2 andthese bunches of electrons induce a corresponding electromagnetic wavein the output resonator 3. The energy exchange between the bunches ofelectrons and the induced electromagnetic wave in the grid-anode gapsdelivers electromagnetic Wave energy to the wave, in a manner well knownto those skilled in the space-charge tube art. Electromagnetic waveenergy can be extracted from the output resonator 3 through the outputcoupling means 3a.

In the above-discussed operation the passive capacity elements 15 serveto maintain the desired operation wherein the electric field maximaoccur in the resonators at the interaction gaps of the space chargecontrol devices 5. Also, the described periodic loading serves to affordmaximum mode separation. This latter function will be better understoodfrom a discussion of the propagation and wave-supporting characteristicsof the periodicallyloaded waveguides provided in the above-describedstructure. In such structure an electromagnetic wave in either of theresonators 2 and 3 is presented with periodically arranged capacitancesin the form of either the cathodesgrid gaps and the passive elements 15in resonator 2 or the grid-anode gaps and the passive elements 15 inresonator 3. Thus, each of the resonators 2 and 3 is, in effect, anelectrically-shorted section of a periodically loaded waveguide with theperiodic loading afforded by alternate interaction gaps of space-chargecontrol tubes and passive capacitive elements.

FIGURE 3 is -an wdiagram and shows the graphical relation of the phaseshift per section of matched periodically-loaded waveguides as afunction of the frequency of an electromagnetic wave within one of suchwaveguides. As seen in FIGURE 3, each of the loaded waveguides hasalower limit of frequency, or lower cut-off frequency, below whichenergy will not be propagated therethrough. As the frequency increasesabove the lower cut-off frequency, propagation becomes possible; and ifthe frequency is continuously increased above cutoff, a frequency willultimately be reached where the spacing between adjacent periodiccapacitances in the periodically-loaded waveguide becomes equal to halfof a waveguide wavelength. At this frequency, the phase shift betweenadjacent capa-citances is equal tol 1r radians. The reilection from acapacitance then reinforces the reflection from the immediatelypreceding periodic capacitance land the overall effect in a longwaveguide is total reflection and no propagation. The matchedperiodicallyloaded waveguide thus serves as a band-pass filter forfrequencies between these upper and lower cut-olf frequencies. Thematched periodically-loaded waveguide also has pass bands and stop bandsat higher frequencies, but they are of no interest for the presentdiscussion.

While the matched periodically-loaded waveguide can support anelectromagnetic wave having a frequency of yany value within the passband, an additional limitation exists when the periodically-loadedwaveguide is made resonant by terminating the ends in short circuits, asis the case for the above-described resonators. Resonance occurs in theshort-circuited periodically-loaded waveguides only at those frequenciesin which the structure is an integral number of loaded guide half wavelengths long and in such waveguides the total phase shift along theguides must thus be an integral multiple of 1r. In other words,resonance occurs only at frequencies at which the difference in phase ofthe wave at two adjacent periodic capacitances is vrn/N Where N is thenumber of sections into which the line is divided by the periodiccapacitances and n is an integer in the interval w=I to n=N. Thus, lf heresonators 2 and 3 are capable of supporting electromagnetic waves onlyof the frequencies indicated at positions 16-23 of FIGURE 3, with eachof these frequencies having a phase shift per sec- OII Of vr/S, 11"/4,31r/8, '1r/2, 51r/2, 31r/4, 71r/8 and 1r r3.- dians, respectively. It isnoted that all of these frequencies lie between the lower cut-olffrequency and the upper cut-E frequency of the lirst pass band of theperiodically-loaded waveguide.

It is known that maximum energy transfer between an electromagnetic waveand an interaction gap occurs when electrons see the greatest possibleintegrated electric ield when passing through the gap. As mentionedabove, the described loading Iincluding alternate lactive and passivegaps and operation of the apparatus at the mentioned predeterminedfrequency are effective for maintaining the apparatus operative stablyin the 1r/2 mode in which the electric field maxima in the waveguidescoincide with the positions of the interaction gaps. Thus, efficiency ismaximized. Also in the 1r/2 mode maximum mode separation is obtained.Additionally, the described operation enables the production of highpower output with the low voltages at which the space-charge controldevices 5 characteristically operate. This enables power production atlevels which are generally not attainable with such devices. Also, itminimizes power supply requirements.

When space-charge control tubes are operated in `a grounded gridfashion, as is the case in the operation of the above-describedapparatus, radio frequency energy accelerates electrons from thecathodes of the tubes across the cathode-grid interaction region. Thisresults in an equivalent positive input conductance in shunt with thecapacitive susceptance of the cathode-control grid electrodes. If, as inaccordance with the present invention, a plurality of such tubes areoperated in a periodicallyloaded input waveguide resonator, thisconductance tends to make the attenuation of the input resonator highand cause the input radio frequency signal not to appear equally in allof the interaction regions defined by the cathodes and the respectivecontrol grids. The abovedescribed offset arrangement shown in FIGURE 2locates the tube interaction gaps and passive elements therebetween on aline spaced parallel to the center line of the input Iwaveguide. Thisavoids excessive attenuation and achieves uniform excitation of theseveral tubes by decoupling the individual unit input admittances fromthe input waveguide resonator 2. The output resonator 3 is centeredabout the control grid-anode interaction rcgions of the devices 5 inorder to achieve maximum energy transfer from the passing electrons tothe standing electromagnetic Wave therein, thus to achieve maximum gainand efficiency.

FIGURE 4 shows a cross-sectional view of another embodiment of theinvention. The apparatus shown therein includes input and outputresonators 25 and 26, respectively, similar to the resonators of thestructure of FIGURE l, but the resonators of FIGURE 4 are supported inspaced parallel relation rather than being juxtaposed and having acommon wall, as is the case in FIGURE 1.

The resonators 2S and 26 include input and output coupling means shownas inductive loops designated 25a and 26a, respectively. Also, eachresonator comprises an electrically-shorted section of waveguide and issuitably adapted for having tetrode-type space-charge control devices 27mounted therein. Each device 27 comprises a suitable envelope structure28 containing a cathode 29, a control grid 30, a screen grid 31 and ananode 32, which electrodes are suitably spaced and mutually insulated.The cathode 29, control grid 30, screen grid 31 and anode 32 areprovided with suitable coaxial contacts 33, 34, 3S and 36, respectively,which, when the devices are mounted in the waveguides, make suitablecoaxial electrical contact with the respective walls of the waveguides.Specifically, the contacts 33 and 34 engage the lower and upper walls,respectively, of the input waveguide 25 and the contacts 35 and 36engage the lower and upper walls, respectively, of the output waveguide26. Thus, the cathode-control grid interaction regions, or gaps, of thetubes are coupled to the input waveguide for interaction between anyelectromagnetic wave energy therein and electron flow across thecathodethe devices 27 can be either discrete detachable structures asillustrated or, if desired, can be constructed integrally with thewaveguides in a single evacuated and hermetically sealed device.

The waveguides 25 and 26 are provided with passive, or dummy, capacitiveelements 37 which are located in the same positions and serve the samefunctions as the capacitive elements 15 of the above described iirstembodiment. Additionally, the same spacing is provided between thedevice 27 and passive elements 37 for periodically loading thewaveguides in the same manner and for the same purpose as describedabove.

Additionally, and as seen in FIGURE 5, the output waveguide 26 iscentered about the screen grid-anode interaction regions of the devices27 and passive elements 37 therebetween in order to achieve maximumenergy transfer to the standing electromagnetic wave induced in theoutput waveguide, thereby to achieve maximum gain and eiciency. However,the input Waveguide ZS is offset relative to the output waveguide andthus the cathode-control grid interaction regions of the devices 27 andpassive elements 37 therebetween are transversely spaced from thelongitudinal center or axis of the input waveguide. In this embodimentalso, the olf-center relationship serves to avoid excessive attenuationof the input signal and achieves uniform excitation of the devices bythat signal by effectively decoupling the individual unit inputadmittances from the input Waveguide.

The operation of the device of FIGURE 4 and 5 is as follows: Anaccelerating D.C. potential is established in any suitable manner (notshown) between the control grids 30 and screen grids 31. The cathodes 29can be maintained at the same potential as the control grids 30 ifdesired and the anodes 32 maintained at the same potential as the screengrids 31. An input signal at the above-mentioned predetermined frequencyis induced in the input resonator 25 through input means 25a. Electronsleave the cathode members 29 under the influence of the positive halfcycles of the induced wave and the leaving electrons, in passing betweenthe control grids 30 and screen grids 31 are accelerated to a relativelyhigh velocity and enter the interaction regions between the screen gridsand the anodes 32 at this relatively high velocity. The passage ofelectrons through the interaction region induces a correspondingstanding electromagnetic wave in the output resonator 26. Maximum energytransfer from the electrons in the screen grid-anode interaction regionsto the electromagnetic wave in the output resonator is obtained if theelectrons enter the interaction regions during the negative half cyclesof the induced electromagnetic wave, whereby the electrons aredecelerated a maximum amount and deliver, or surrender, the maximumpossible energy to the electromagnetic wave.

Either the triode apparatus of FIGURES 1 and 2 or the tetrode apparatusof FIGURES 4 and 5 can be operated in class C operation, so as toprovide maximum eiciency, by providing suitable biasing means upon thecathode members of the devices therein. When so operated, the biasingvoltage prevents electrons from leaving the cathodes except during theshort portion of the input cycles centered about the positive crest ofthe alternating control-grid-cathode field. The electrons therefor enterthe output resonators in discrete groups or bunches so as to provide themost eflicient energy transfer to the output resonator.

Either of the devices of FIGURES 1 `and 2 or FIG- URES 4 and 5 can beoperated as an amplifier to amplify an input signal or can be operatedas an oscillator so as to constitute a source of electromagnetic wavepower. Any of the suitable feedback arrangements known to those skilledin the art can be utilized in producing suitable oscillation in thedevices.

While the invention is thus shown and the modes of operation of specicembodiments described, the invention is not limited to use in theseshown embodiments. Instead, the foregoing will suggest manymodifications to those skilled in the art and which will lie within thespirit and scope of the invention. It is specifically intended that theinvention include structures wherein the input and output resonators arerelatively ofset both with and without the passive members positionedbetween adjacent active elements or devices. Also, the invention is notlimited to use in structures having only four electron discharge devicesmounted therein, `but can be used in a structure having any desirednumber of such devices. Further, the invention is not limited to use instructures in which the input and output resonators are straightsections of rectangular waveguides, but can equally well be used indevices in which the resonators are curved sections of waveguide andwherein the cross-sectional conguration of the waveguide is other thanrectangular. It is thus intended that the invention be limited in scopeonly by the appended claims.

What is claimed as new and desired to be secured by Letters Patent ofthe United States is:

1. A multiple beam radio frequency apparatus comprising a pair ofparallel resonant input and output waveguides each periodically loadedby alternate space-charge control devices and passive capacitiveelements, said devices each including a cathode-grid gap coupled to oneof said waveguides and a correspondingly directly opposite grid-anodegap coupled to the other of said waveguides, means for establishing insaid one waveguide a standing electromagnetic wave having an electricfield maxima occurring at each cathode-grid gap and a minima occurringat each said passive element therein, whereby an amplifiedelectromagnetic wave is induced in said other waveguide corresponding tosaid wave in said one waveguide and having electric field maxima andminima occurring, respectively, at said grid-anode gaps and passiveelements therein, said waveguides being positioned in adjacentrelationship so that the center line of one is in spaced parallel andtransverse relationship to the corresponding center line of the other,said space charge devices being positioned and extending into each saidwaveguide so that each said device is along the center line of said onewaveguide but transversely spaced from the said corresponding centerline of said other waveguide and means for extracting radio frequencyenergy from said other waveguide.

2. A multiple beam radio frequency apparatus comprising a pair ofparallel resonant offset waveguides each periodically loaded by meansincluding a plurality of alternate equally-spaced electric dischargedevices and passive capacitive elements, said devices each including oneinteraction gap coupled to one of said waveguides and anothercorresponding opposite and concentric interaction gap coupled to theother -of said waveguides, said one interaction gap being located offthe center line of said one waveguide and its concentrically oppositeinteraction gap being located on the center line of said otherwaveguide, and means for establishing a standing electromagnetic wave insaid one waveguide and extracting energy from said other waveguide.

3. A multiple beam radio frequency apparatus comprising a pair ofparallel resonant offset input and output waveguides each periodicallyloaded by means including a plurality of equally-spaced space-chargecontrol devices and alternate passive capacitive elements, said deviceseach including a cathode grid interaction gap coupled to said inputwaveguide and a grid-anode interaction gap coupled to said outputwaveguide, said cathode-grid gap being located off the center line ofsaid input waveguide and said grid-anode gap being located in saidoutput waveguide in concentrically opposite relationship to saidcathode-grid gap and on the center line of said output waveguide, andmeans for establishing a standing electromagnetic wave 1n said inputwaveguide and extracting energy from said output waveguide.

fl.l A multiple beam radio frequency apparatus comprislng a pair ofparallel resonant elongated input and output waveguides eachperiodically loaded by plural alternate space-charge control devices andplural passive capacitive elements, said devices each including acathode-grid gap coupled to said input waveguide at a point spaced fromthe center line thereof and an opposite corresponding concentricgrid-anode gap coupled to said output waveguide directly opposite saidcathode-grid gap and, at the center line thereof, means for establishingin said input waveguide a standing electromagnetic wave having anelectric field maxima occurring at each said cathode-grid gaps and aminima occurring at each said passive elements therein, whereby anamplified electromagnetic wave is induced in said output waveguidecorresponding to said wave 1n said input waveguide and having electriceld maxima and minima occurring, respectively, at said gridanode gapsand passive elements therein, and means for extracting radio frequencyenergy from said output waveguide.

5. A multiple beam radio frequency apparatus compising a pair ofparallel resonant waveguides having a cornmon wall section, each saidwaveguide being periodically loaded by means including a plurality ofalternate equallyspaced space-charge control triodes, said triodes andpassive gap elements each including a cathode-grid gap coupled to one ofsaid waveguides at a point spaced transversely from the center linethereof, and a grid-anode gap directly opposite said cathode-grid gapand coupled to the other of said waveguides on the center line thereof,and means for establishing a standing electrmagnetic wave in said onewaveguide and extracting energy from said other waveguide.

6. Radio frequency apparatus according to claim 5, wherein the means forperiodically loading said waveguides includes a passive capacitiveelement positioned midway between each adjacent pair of space-chargecontrol triodes in each said waveguide, the capacitive elements in eachwaveguide being in concentric and opposite relationship to each other,and along the center line con taining the said triodes.

7. A multiple beam radio frequency apparatus comprising a pair ofadjacent spaced parallel longitudinally extending waveguides, each saidwaveguide being periodically loaded by means including a row of aplurality of alternate equally-spaced space-charge control tetrodes andpassive capacitive elements, said tetrodes each including acathode-control grid gap coupled to one of said waveguides at a pointspaced transversely from Ithe center longitudinal axis thereof and anopposite screen grid-anode gap coupled to the other of said waveguidesalong the 1ongitudinal axis thereof, and means for establishing astanding electromagnetic wave in said one waveguide and eX- tractingenergy from said other waveguide.

8. A multiple beam radio frequency apparatus according to claim 7,wherein the means for periodically loading said waveguides includes arow of passive capacitive element positioned midway between eachadjacent pair of space-charge control tetrodes in each said waveguides,the said capacitive element in each waveguide being in opposite andconcentric relationship to each other.

9. A multiple beam klystron apparatus comprising in combination,

(a) a pair of adjacent input and output longitudinally extendingwaveguides of substantially rectangular and identical cross-section,

(b) each of said waveguides being periodically loaded by a row ofalternating equally spaced plural spacecharge control devices and pluralpassive capacitive gap elements,

(c) said waveguides being positioned in transverse olfset lrelationshipto eachother,

(d) each of said space charge control devices including a cathode-gridgap in said input waveguide and anodegrid gap in said output waveguide,

(e) said row of space charge control devices having the anode-grid gapsthereof positioned in a longitudinal plane extending through thelongitudinal axis of said output waveguide,

(f) said row of space charge control devices having a cathode-grid gapthereof in concentric and opposite relationship to said anode-grid gapand positioned in said input waveguide -so that the said cathode-gridgaps are positioned in a plane extending through the longitudinal axisof said input waveguide and parallel to the said longitudinal plane ofsaid output waveguide,

(g) means establishing a standing electromagnetic wave in said inputwaveguide having an electrical eld maxima occurring at each saidspace-charge control device ,and a minima occurring at each said passivegap element ltherein whereby an amplified electromagnetic wave isinduced in said output waveguide corresponding to said wave in saidinput waveguide,

(h) and output means for extracting radio frequency energy from saidoutput waveguide.

References Cited by the Examiner UNITED STATES PATENTS 2,353,742 7/ 1944McArthur 315-516 2,745,910 5/1956 Dehn 333-83 X 2,899,647 4/ 1959Willwacher etal. 333--83 X 2,920,229 1/ 1960 Clarke 315-516 2,920,286 1/1960 Havstad 333-83 X HERMAN KARL SAALBACH, Primary Examiner.

ARTHUR GAUSS, S. CHATMON, JR., Examiners.

1. A MULTIPLE BEAM RADIO FREQUENCY APPARATUS COMPRISING A PAIR OFPARALLEL RESONANT INPUT AND OUTPUT WAVEGUIDES EACH PERIODICALLY LOADEDBY ALTERNATE SPACE-CHARGE CONTROL DEVICES AND PASSIVE CAPACITIVEELEMENTS, SAID DEVICES EACH INCLUDING A CATHODE-GRID GAP COUPLED TO ONEOF SAID WAVEGUIDES AND A CORRESPONDINGLY DIRECTLY OPPOSITE GRID-ANODEGAP COUPLED TO THE OTHER OF SAID WAVEGUIDES, MEANS FOR ESTABLISHING INSAID ONE WAVEGUIDE A STANDING ELECTROMAGNETIC WAVE HAVING AN ELECTRICFIELD MAXIMA OCCURRING AT EACH CATHODE-GRID GAP AND A MINIMA OCCURRINGAT EACH SAID PASSIVE ELEMENT THEREIN, WHEREBY AN AMPLIFIEDELECTROMAGNETIC WAVE IS INDUCED IN SAID OTHER WAVEGUIDE CORRESPONDING TOSAID WAVE IN SAID ONE WAVEGUIDE AND HAVING ELECTRIC FIELD MAXIMA ANDMINIMA OCCURRING, RESPECTIVELY, AT EACH GRID-ANODE GAPS AND PASSIVEELEMENTS THEREIN, SAID WAVEGUIDES BEING POSITIONED IN ADJACENTRELATIONSHIP SO THAT THE CNETER LINE OF ONE IS IN SPACED PARALLEL ANDTRANSVERSE RELATIONSHIP TO THE CORRESPONDING CENTER LINE OF THE OTHER,SAID SPACE CHARGE DEVICES BEING POSITIONED AND EXTENDING INTO EACH SAIDWAVEGUIDE SO THAT EACH SAID DEVICE IS ALONG THE CENTER LINE OF SAID ONEWAVEGUIDE BUT TRANSVERSELY SPACED FROM THE SAID CORRESPONDING CENTERLINE OF SAID OTHER WAVEGUIDE AND MEANS FOR EXTRACTING RADIO FREQUENCYENERGY FROM SAID OTHER WAVEGUIDE.